This application claims the priority of German patent document 100 11 404.0, filed Mar. 9, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device for identification of an external power supply in a vehicle, and particularly for identifying external starting of a motor vehicle which has an electrical on-board power supply system with a battery for providing an on-board power supply system voltage. In addition, the invention relates to a method for operation of such a device.
Safety-relevant functions in vehicles, such as for example the very recently developed electric brake, are increasingly being separately electrically powered. In order to assure the functionality of such components at all times, they must receive an uninterrupted supply of electrical power. For this purpose, in vehicles it is known to provide two energy sources, namely a battery and a generator.
Since the life of a conventional lead-acid battery is generally shorter than the life of the vehicle, situations regularly arise in which only one of the two energy sources can still operate. In most cases, the generator will have a longer life than the battery in this arrangement.
One method for monitoring the serviceability of a battery by means of its battery voltage is disclosed in German patent document DE 195 17 709. The result of the monitoring and the data determined in the process are in this case used, in particular, to decide whether a machine which is connected to the battery will or will not be allowed to operate further.
If the generator is damaged or overloaded when the battery is discharged or defective, the supply to the loads is then no longer ensured and the vehicle can enter a safety-critical state. The generator can be overloaded when more loads are connected than it can nominally supply. For this reason, emergency measures must be taken which, firstly, warn the driver and, secondly, also keep the on-board power supply system in an operationally safe state for as long as possible. The latter can be achieved by retaining only a few important loads in a switched on or connected state.
Furthermore, when the battery is discharged or defective, the vehicle can no longer be started. Thus, starting capability may be regarded as a criterion for the state of the battery energy source. However, in situations such as this, a second vehicle is often used as a starting aid, simulating, so to speak, an intact battery. In this situation, the safety measures mentioned above are not carried out and the warning or stabilization measures do not come into play. For this reason, external starting must be identified.
All that is known in this context from German patent document DE 196 49 392 C2 is to provide a connecting cable for voltage maintenance to be supplied by an external power source having an electronic circuit, which checks that the cable has been connected correctly. In German patent document DE 298 06 441, a warning lamp is provided to indicate that an additional or external energy storage unit has been connected to the vehicle on-board power supply system.
One object of the invention is thus to provide a method and apparatus of the type described initially, which can detect the connection of an external power supply and the performance of external starting, as reliably as possible.
Another object of the invention is to provide such a device and a corresponding method, which can be produced easily and cost-effectively.
These and other objects and advantages are achieved by the method and apparatus according to the invention, in which a monitoring unit is arranged between the battery and the on-board power supply system, and includes a sensor for detection or monitoring of the on-board power supply system voltage, or interacts with such a sensor. The invention is based, in particular, on the proposition that a change in the on-board power supply system voltage and/or in the battery parameters occurs when electrical contact is made between an external battery and a vehicle battery. According to the invention, this change is detected and is evaluated as a function of various parameters relating to external starting. In contrast to the abovementioned prior art, the on-board power supply system voltage is used, in particular, rather than the battery voltage, as the output variable for assessment.
In addition, it is possible to provide the monitoring unit with a sensor for detection of the electric current flowing out of the battery and/or the electric current flowing into the on-board power supply system, or to interact with such a sensor. Together with the detected on-board power supply system voltage, this also allows changes in the on-board power supply system load to be recognized and, advantageously, to be taken into account in the evaluation.
It is also possible to provide the monitoring unit with a sensor for detecting the operating temperature of the battery, or to interact with such a sensor. In principle, the connection of two batteries electrically represents a parallel circuit, as a result of which the total internal resistance of the batteries is reduced. The internal resistance can in this case be measured by a current and voltage measurement using the said sensors. The reduced internal resistance also results in an increase in the current flowing through the battery, which is also associated with a measurable increase in the battery temperature.
This evaluation process can be automated by providing the monitoring unit with a computer unit, in particular a microcontroller, for determination of changes in the electrical on-board power supply system variables.
Any change in the on-board power supply system load can advantageously be recognized by a controllable switch which interacts with the microcontroller, or alternatively by means of vehicle data which are provided via a vehicle CAN bus and are transmitted to the microcontroller.
A further embodiment envisages a timer for detection of a time duration (particularly a minimum duration) of any drop in voltage which may occur in the on-board power supply system voltage. Together with recognition that the monitoring unit is being started or restarted after a power-on reset, the timer makes it possible to detect a total loss of battery voltage, in order to distinguish between this and brief drops in voltage.
It is furthermore possible to provide for the monitoring unit to enter a sleep mode after a time interval which can be predetermined, thereby saving energy for supplying the unit. In this case, means can be provided for storing an on-board power supply system voltage value (particularly a read-only memory), and means can be provided for comparing the stored value with an approximately sensed present on-board power supply system voltage. When the on-board power supply system voltage is in a stable state, then, once the monitoring unit has been xe2x80x9cawakenedxe2x80x9d, only minor changes can occur, in principle, in the voltage, compared with the stored value.
The method according to the invention, for operating the above-mentioned device in a motor vehicle having an electrical voltage generator operated by an engine, includes in particular, the following:
a) monitoring at least one of the electrical on-board power supply system variables and/or the state of the monitoring unit during a starting phase of the monitoring unit;
b) monitoring at least one of the electrical on-board power supply system variables before starting the engine; and
c) monitoring at least one of the battery state variables during an engine starting phase.
In the method, an additional step d) can now be provided by monitoring at least one of the battery state variables once the engine has been successfully started until the vehicle starts to be driven, in order to detect whether the disconnection of an external starting cable is identified. Specifically, according to the invention, after an external start has been carried out by means of an electrical starting jumper cable, the starting jumper cable is finally disconnected once again on both vehicles. In this case, the cable is never disconnected until after starting of the engine in the vehicle to which starting assistance is being given, and this implies measurable changes in the battery state variables, such as the battery voltage. After successful engine starting, the generator in the vehicle to which starting assistance is being given will supply a current, the majority of which flows into the battery. Furthermore, current can flow into the battery in the vehicle providing the starting assistance. If the starting jumper cable is now disconnected in this situation, then the measured current into the battery falls suddenly. This can be identified as disconnection of the starting jumper cable, and thus as external starting. This routine ends when the vehicle is driven off. This further monitoring step thus increases considerably the reliability of identification of external starting.
Furthermore, in addition, a switch signal from the vehicle trunk lid or the hood can be evaluated, as a plausibility factor, in order to detect whether either of them has been opened. Depending on whether the battery is arranged in the engine compartment or in the trunk, one of these sensors will indicate an xe2x80x9copen hood or trunk lidxe2x80x9d if the battery is accessed, for example in order to connect a starting jumper cable. Thus, so to speak, an open hood or trunk lid represents a necessary but insufficient condition for external starting to take place.
The step or steps a) is or are in this case advantageously carried out only once during the starting of the monitoring unit while, in contrast, steps b) and c) are carried out in a loop until a defined final state is reached.
The monitoring unit can be started from various states. Normally, it is either in an operating mode or in the abovementioned sleep mode. (That is, the unit is in a rest state, but reacts to changes in the vehicle state or to internal wake-up signals.) Thus, according to the invention, step a) can also be used to check whether the monitoring unit is being activated from a sleep mode or by means of a power-on reset, with a further check being carried out in the case of a power-on reset to determine whether the drop in voltage has lasted for more than a minimum period, which can be predetermined. Furthermore, it is possible to provide for a most recently measured on-board power supply system voltage and/or an on-board power supply system voltage detected cyclically by means of regular waking up from the sleep mode to be stored before the monitoring unit enters the sleep mode, and for a regularly detected present on-board power supply system voltage to be compared with the stored value.
In the situation where the battery is being charged, the charging process is ended after a certain time without the engine having been started. After this, the on-board power supply system voltage falls once again. However, the drop in voltage on its own is not sufficient to allow identification that an external energy source has been disconnected. According to the invention, it is thus possible to provide for the on-board power supply system load also to be detected and to be compared appropriately.
In one exemplary embodiment, step b) is used to check whether the on-board power supply system voltage when the engine is not running, is greater than a first threshold value that is between a battery normal voltage and a generator normal voltage, and, if so, whether an engine start will be carried out within a first time window which can be predetermined. For external starting, a connection between the two vehicle batteries is normally produced first of all, and the engine of the vehicle to which starting assistance is being given is then started, as a result of which its generator provides a voltage of about 14 V. This in turn likewise leads to the on-board power supply system voltage of the vehicle to which starting assistance is being given being increased to about 14 V, or to a voltage value between the battery normal value of about 12.5 V and the voltage of 14 V supplied by the generator. If the on-board power supply system voltage in the vehicle to which starting assistance is being given now exceeds the first threshold value mentioned when the engine in the vehicle is stationary, then an external energy source must necessarily be present.
If no engine start now takes place, all that is happening is that the battery is being charged. If the charging process is then interrupted, the on-board power supply system voltage falls once again. Thus, according to the invention, if no engine start takes place within the first time window, another check is carried out to determine whether the on-board power supply system voltage has fallen again, without the on-board power supply system load having changed.
If, however, the voltage level is below the first threshold value, then a further check is made to determine whether the on-board power supply system voltage (when the engine is not running) has increased within a second (predeterminable) time window of a few seconds (particularly about 5-10 seconds). Since a vehicle which needs to be started externally has a discharged battery, its rest voltage will be relatively low. If a second battery is now connected to this battery, the voltage is equalized, which briefly raises the voltage in the on-board power supply system to which the external start is being given.
To confirm the plausibility of the abovementioned voltage increase, an additional check can be made to determine whether the on-board power supply voltage is greater than a second threshold value. This advantageously makes it possible to avoid recovery of the battery voltage after a load, for example a starter, has been switched off being assessed as the connection of an external energy source.
According to a further exemplary embodiment, step b) is furthermore used to check whether the on-board power supply system voltage is greater than a third threshold value, with the on-board power supply system load remaining constant and without the generator supplying any power. If the load on the on-board power supply system remains unchanged, or does not increase, then it is impossible for a voltage greater than the third threshold value to occur. If a voltage greater than this threshold value is measured, without the generator supplying any current, then it must be assumed that there is an external energy supply.
A further exemplary embodiment provides that, in step c), the electrical internal resistance of the battery is detected while engine starting is taking place, in particular via a current and voltage measurement using the said sensors (possibly as a function of temperature) and is buffer-stored, and a subsequent check is carried out to determine whether the presently measured internal resistance is less than the stored value. In the process, it is also possible to check whether the present value is considerably less than during a recently carried out failed starting attempt, or whether the value is less than a predetermined value. In the electrical sense, connection of the two batteries results in the respective internal resistances of the two voltage sources being connected in parallel. In consequence, the total internal resistance of the two batteries is reduced. If a considerably reduced battery internal resistance is now identified during another starting attempt once an external energy source has been connected, without this having been identified in step b), then, according to the invention, external starting is deduced. In addition, the battery operating temperature can be detected and checked to determine whether the operating temperature is greater than the detected value.
The detected internal resistance and/or battery operating temperature in a first starting attempt can advantageously be stored, and the battery parameters of the most recent starting attempt can be used as a reference.
According to the invention, an externally caused push against a motor vehicle (for example when a motor vehicle is being towed) can be identified by monitoring the wheel rotation speed and the engine rotation speed of the motor vehicle. If a wheel rotation speed value greater than 0 is detected when engine rotation speed value=0, it is assumed that the motor vehicle is being propelled by an external source (in particular that the motor vehicle is being towed). This identification can in this case advantageously be used as an additional monitoring step in the method mentioned above.
The invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the drawings, and with the same reference symbols being used for functionally identical or similar features.